Influence of transcutaneous vagus nerve stimulation on cardiac vagal activity: Not different from sham stimulation and no effect of stimulation intensity

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The present study investigated the effects of transcutaneous vagus nerve stimulation on cardiac
vagal activity, the activity of the vagus nerve regulating cardiac functioning. We applied
stimulation on the left cymba conchae and tested the effects of different stimulation intensities
on a vagally-mediated heart rate variability parameter (i.e., the root mean square of successive
differences) as well as on subjective ratings of strength of perceived stimulation intensity
and unpleasantness due to the stimulation. Three experiments (within-subject designs, M =
61 healthy participants each) were carried out: In Experiment 1, to choose one fixed stimulation
intensity for the subsequent studies, we compared three preset stimulation intensities
(i.e., 0.5, 1.0 and 1.5 mA) with each other. In Experiment 2, we compared the set stimulation
method with the free stimulation method, in which the participants were instructed to freely
choose an intensity. In Experiment 3, to control for placebo effects, we compared both methods
(i.e., set stimulation vs. free stimulation) with their respective sham stimulations. In the
three experiments, an increase of cardiac vagal activity was found from resting to the stimulation
phases. However, this increase in cardiac vagal activity was not dependent on stimulation
intensity (Experiment 1), the method used to stimulate (i.e., set vs. free; Experiment 2),
or whether stimulation was active or sham (Experiment 3). This pattern of results was solidly
supported by Bayesian estimations. On the subjective level, higher stimulation intensities
were perceived as significantly stronger and a stronger stimulation was generally also perceived
as more unpleasant. The results suggest that cardiac vagal activity may be similarly
influenced by afferent vagal stimuli triggered by active and sham stimulation with different
stimulation intensities. Potential explanations for these findings and its implications for future
research with tVNS are discussed.
ZeitschriftPloS one
PublikationsstatusVeröffentlicht - 24.10.2019

ID: 4906750


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